Systems, apparatuses, and methods for treating drilling fluid

ABSTRACT

A method for treating drilling mud includes directing a first flow portion of a flow of drilling mud to a decanter centrifuge, directing a second flow portion of the flow of drilling mud to a solids particle recovery hopper, and separating an underflow from the first flow portion with the decanter centrifuge, wherein the underflow includes first solids particles having a first density. The underflow is directed to the solids particle recovery hopper, the underflow is mixed with the second flow portion in the solids particle recovery hopper, and a flow of the mixed underflow and second flow portion is directed from the solids particle recovery hopper to an active mud tank.

BACKGROUND 1. Field of the Disclosure

The present subject matter is generally directed to drilling operations, and in particular, to systems, apparatuses, and methods that may be used for treating drilling fluid so as to recover beneficial solids particles, such as barite and the like, from the drilling fluid.

2. Description of the Related Art

During a typical well drilling operation, such as when an oil and gas well is drilled into the earth, a drilling mud circulation and recovery system is generally used to circulate drilling fluid, i.e., drilling mud, into and out of a wellbore. The drilling mud provides many functions and serves many useful purposes during the drilling operation, such as, for example, removing drill cuttings from the well, controlling formation pressures and wellbore stability during drilling, sealing permeable formations, transmitting hydraulic energy to the drilling tools and bit, and cooling, lubricating, and supporting the drill bit and drill assembly during the drilling operations.

In order to control formation pressures and wellbore stability during drilling operations, the drilling mud must have a great enough density so that the weight of the column of fluid at any point in the wellbore is sufficient to prevent the local geological forces in the surrounding formation from collapsing the wellbore. Additionally, the density of drilling mud must also be great enough to prevent an undesirable ingress of fluid that may be present in the surrounding formation from entering the wellbore, which can tend to migrate to the surface and increase the potential for a well blowout scenario. Accordingly, the drilling mud is generally designed and formulated, and in particular the density or “weight” of the mud is often adjusted, in view of these various operating scenarios with a goal of providing a more reliable, consistent, and predictable overall drilling operation.

Drilling muds commonly include many different types of desirable solid particles that aid in performing one or more of the functions and purposes outlined above. These solids particles used in drilling muds may have one or more particular properties which makes their presence in a particular drilling mud mixture desirable and beneficial. For example, in certain applications, some solids particles may need to be of a certain size or size range, which may be useful in sealing off more highly permeable formations so as to prevent the loss of valuable drilling fluid into the formation—so-called “lost circulation materials.” In other applications, such as when relatively high wellbore pressures are anticipated or encountered, other solids particles may need to be of a certain density or “weight” so as to control and balance forces within the wellbore, which may be added to the drilling mud as necessary so as to guard against wellbore collapse or even a well blowout during the drilling operation.

In some drilling applications, the base fluid of the drilling mud—which may substantially be water, a hydrocarbon-based fluid, a synthetic hydrocarbon replacement fluid, and/or some combination thereof—may be used to create what is sometimes referred to as an “unweighted” drilling mud. Typically, the base fluid is the primary constituent in an unweighted drilling mud, and any suspended solids particles present in the unweighted drilling mud would usually only include so-called “native solids,” which are generally any dispersed clays, sand, chert, and/or other rock that originates from formations being drilled. In general, unweighted drilling muds are most often used in relatively shallow drilling operations when the wellbore formation pressures are typically lower than the competing hydrostatic head pressure of the drilling fluid. However, in drilling applications where the formation pressures are high enough to exceed the hydrostatic head pressure of the drilling fluid, solids particles having a greater density, or specific gravity, must be added to the drilling mud mixture so as to increase the overall density of the mud, thus creating what is often referred to as a “weighted” drilling mud.

For example, in some applications, high density particulate materials such as barium sulfate, or barite, (BaSO₄), are often used for this purpose, as their greater unit volumetric weight serves to counterbalance the high formation pressures and/or the mechanical forces that are often caused by formations that would otherwise begin sloughing during the drilling process. Furthermore, in at least some cases, solids particles may be added to the drilling mud based on a combination of the particle size and density, such as when a specific combination of the two properties may be desirable. As would be appreciated by those of ordinary skill, the drilling mud in general, and the added solid particles in particular, can often be very expensive. As such, in some applications, various systems and processes have been implemented so that the desirable—and valuable—solids particles can be recovered and re-used during the ongoing drilling cycle.

Once the drilling mud has served its initial purposes downhole, the mud is then circulated back up and out of the well so that it can carry the drill cuttings that are removed from the advancing wellbore during the drilling operation up to the surface. As may be appreciated, the drill cuttings that are generated during the drilling operation, which are also solids particles, are generally thoroughly mixed together with other beneficial solids particles that may have been added to the base fluid so as to make up the drilling mud. Therefore, these drill cuttings must be separated from the desirable solids particles which, in the case of weighted drilling muds would be higher density solids particles, such as barite and the like. In the best possible drilling scenario, it is advantageous for the drill cuttings to be substantially larger than the desirable solids particles making up the drilling mud, thus enabling a substantial portion of the drill cuttings to be removed during a primary separation step using vibratory separator devices that separate particles based upon size, such as shale shakers and the like. However, in most applications, a portion of the drill cuttings returning with the drilling mud are similar in size, or even smaller than, at least some of the desirable solids particles contained in the drilling mud, in which case secondary separation devices, such as hydrocyclones and/or decanter centrifuges and the like, are often employed so as to obtain further particle separation.

For example, in accordance with API Specification 13A, barite that is added to drilling mud is required to be made up of particles having a particle size distribution wherein no more than 3 weight percent is coarser than 75 microns and no more than 30 weight percent is finer than 6 microns. As such, the majority of the barite particles that are used in drilling mud have a particle size that ranges from 6-75 microns, with the allowances outside of this range as noted above. Furthermore, the median particle size in this distribution range is typically on the order of around 50 microns. When using a shale shaker or other vibratory separator, better operational proficiency is achieved by the machines when the size of the drill cuttings particles are at least twice that of the valuable solids particles—e.g., barite—that are desirable to keep in the drilling mud mixture. Therefore, drill cuttings particles that are 150 microns or larger can generally be separated rather efficiently from particles such as barite using well known and commonly available screen separation technology.

However, it should be appreciated that while the sizes of a large majority of the drill cuttings particles enable them to be separated with machines that utilize vibratory screening techniques, such as shale shakers and the like, the sizes of many solids particles do not always conveniently fall within the size range that permits such relatively easy separation, e.g., the 150 micron size threshold noted above. The simple reason for this is that there are many factors that can influence the eventual size of drill cuttings particles returned with the drilling mud, such as: formation lithology (different rocks/minerals that are encountered as the wellbore progresses through different formation strata); type of drill bit used (PDC bits cut or shear rock; roller-cone bits crush rock); weight on bit (downward force exerted on the bit by gravity and/or mechanical forces); drilling rate (feet per hour), and the like. Accordingly, the sizes of at least some of the drill cuttings particles will fall squarely within the size range of the drilling mud's desirable solids particles, such as the 6-75 micron size range of barite particles, as noted above.

There are a variety of reasons why it is desirable, and even necessary, to remove as many of the drill cuttings particles from the drilling mud mixture as possible. A first reason would be so as to control and/or maintain the drilling mud chemistry and composition within a desirable range as consistently as possible. For example, the presence of drill cuttings particles in the drilling mud mixture may have a significant effect on the weight of the mud, which could potentially lead to wellbore collapse, and/or a blowout scenario associated with possibly hazardous overpressure conditions within the well. More specifically, because the specific gravity of the drill cuttings particles (that is, the ratio of the drill cuttings particle density to that of water) are normally significantly lower than that of the desired solids particles in the drilling mud, e.g., barite, then the presence of cuttings particles left in the mud by the typical solids removal processes can cause the weight of the drilling mud to be lower than required when the cuttings particles displace the barite. Mineralogically pure barite, or barium sulfate, has a density of about 4.5 gm/cm³ (or a specific gravity of 4.5), whereas the types of cuttings materials that are most typically encountered during drilling operations have a specific gravity that is less than 3.2, and generally falls in the range of about 2.5 to 3.0.

Additionally, the presence of undesirable solids materials in the drilling mud can also have an adverse effect on the flow and/or hydraulic characteristics of the mud, which could thus potentially have a detrimental influence the operational efficiency of the hydraulically driven downhole tools, lubrication and cooling of the drill bit, and the like. Furthermore, depending on the types of materials (e.g., rocks/minerals) that make up the drill cuttings, the drill cuttings particles can be highly abrasive, and therefore could be damaging to the drilling mud circulation equipment, such as mud pumps, seals, valves, and the like. In such cases, expensive drilling downtime may be encountered during the repair and/or replacement of inordinately worn or damaged equipment. Accordingly, rig operators generally go to great lengths to remove as many of the returned drill cuttings particles from the drilling mud as is possible. Furthermore, in the case of weighted drilling muds, operators also make every reasonable effort to recover and re-use as much of the high density (e.g., barite) particulate material as may be economically feasible. To that end, various systems and methods have been employed in an effort to separate high density solids particles from low density drill cuttings particles.

Barite recovery in many prior art applications is generally performed after at least a primary separation step based on particle size has been performed, for example, by using vibratory separator screening systems such as shale shakers. Typically, the prior art method of recovering and re-using the beneficial high density particles (e.g., barite) that have been added to weighted drilling mud involves a three-step approach, which includes: 1) removing barite from the spent (returned) drilling fluid; 2) removing the detrimental low-density solids (small-sized drill cuttings particles) from the drilling fluid; and 3) returning the cleaned drilling mud and recovered barite to the drilling rig's active mud system for re-use. Typically, the solid particle removal steps noted above are performed using decanter centrifuges, which apply centrifugal forces to the drilling fluid so as to separate heavier/more dense solid particles from lighter/less dense fluids. The operation of decanter centrifuges is well known to those having ordinary skill in the art and therefore will not be described in detail herein other than as may be necessary to convey the operating principles of exemplary prior art barite recovery systems.

When a weighted drilling mud is used during drilling operations, both the beneficial high density (e.g., barite) particles and detrimental low density (drill cuttings) particles will be present in the spent drilling mud after it has been returned from a drilled wellbore. When a decanter centrifuge receives the spent drilling mud containing both high and low density particles and is operated to separate the drill cuttings (low density) solids particles from the mud, the barite particles will also be removed during the same operation, since the centrifugal forces imposed on the low density particles will also cause the higher density particles to separate from the fluid. In order to avoid simultaneously separating the high and low density particles from the spent drilling mud during the same solids separation step, typical barite recovery systems utilize two decanter centrifuges that are arranged in a series operation so as to first remove the higher density barite particles from the drilling mud in a first centrifuge, after which the lower density drill cuttings particles are moved from the mud in a second centrifuge.

Due to their higher relative density, or specific gravity, barite particles will more readily drop out of the drilling mud than will the lower density drill cuttings particles when subjected to the same level of centrifugal force. As such, a lower centrifugal force is required to remove the high density bathe particles than is required to remove the low density drill cuttings particles, which is used to advantage in the typical prior art barite recovery systems. In such systems, the first decanter centrifuge is operated at a substantially lower rotational velocity (RPM) than the second centrifuge, and thus a lower centrifugal force is created within the first centrifuge than within the second centrifuge. Accordingly, the lower centrifugal force created within the first decanter centrifuge will be sufficient to remove the higher density barite particles, but will be less effective in removing the lower density drill cuttings particles. The fluid effluent, or overflow, exiting the first centrifuge is therefore laden with minimal amounts of the higher density barite particles and relatively high levels of lower specific gravity solids, such as drill cuttings particles. The overflow fluid is then directed to the second decanter centrifuge for further separation processing. As noted previously, the second decanter centrifuge is operated at a substantially higher rotational speed (RPM) than the first decanter centrifuge, which in turn applies a substantially greater centrifugal force on the overflow fluid received from the first centrifuge. In this way, the removal of lower density drill cuttings particles from the drilling mud can be maximized, after which the cleaned mud is returned to the drilling rig's active mud system.

FIGS. 1A-1C are schematic flow diagrams that illustrate a prior art drilling mud treatment system 100 that includes a solids removal and recovery system 170 that can be configured to treat both weighted and unweighted drilling fluids. In particular, the solids removal and recovery system 170 shown in FIG. 1A is in an operational configuration that allows desirable high specific gravity particles, e.g., barite, to be recovered from a drilling mud 110 and returned the recovered barite to the active mud system for re-use in further drilling operations. In some instances, the solids removal and recovery system 170 may be referred to herein as a barite recovery system 170 for simplicity.

As shown in FIG. 1A, drilling mud 110 that is returned from a drilled wellbore (not shown) flows through a spent mud flow line 102 to a primary solids separation apparatus 104, such as a shale shaker and the like, for an initial separation step. As the drilling mud 110 passes through the shale shaker 104, larger drilling cuttings 107 are separated from the mud 110 and directed to a drilling cuttings tank or pit 108. The portions of the drilling mud 110 passing through the various screening decks of the shale shaker 104 flow down to a sump 106, and from there are directed to the active mud system tank or pit 112 for further processing.

In some configurations of the drilling mud treatment system 100, a flow of the drilling mud 110 may be directed through one or more intermediate mud treatment and/or solids separation apparatuses, which are collectively depicted schematically in FIG. 1A as system 160. For example, the system 160 can include an apparatus for removing entrained gases from the drilling mud 110 (e.g., vacuum or atmospheric degasser), as well as apparatus(es) for removing sand and/or silt from the mud 110 (e.g., desander and/or desilter hydrocyclones). It should be appreciated that the design and operation of such additional treatment and/or separation apparatuses is well known in the art, and as such will not be described further.

As noted previously, the barite recovery system 170 schematically depicted in FIG. 1A is configured for recovering barite from the drilling mud 110 for re-use in further drilling operations. As shown in FIG. 1A, the barite recovery system 170 includes first and second decanter centrifuges 124 and 144, both of which are operated to remove solids particles from drilling mud 110. The barite recovery system 170 also includes a barite mixing tank 134 that is used to temporarily store and blend barite that has been recovered from the drilling mud 110 during the barite recovery process, as well as first and second solids disposal pits or tanks 132 and 150 that can be used for temporary storage of the solids that are removed from the mud 110 using the respective first and second centrifuges 124, 144, prior to eventual disposal. Furthermore, the barite recovery system 170 includes a plurality of pumps 120, 138, 140, and 145 are used to generate various flows of drilling mud 110 through the system 170, as well as a plurality of flow redirection devices 130, 135, and 142 that can be used to direct the various flows of drilling mud 110 to specific apparatuses of the system 170, as will be further described below.

As shown in FIG. 1A, during a barite recovery operation, a first pump 120 is used to generate a flow 113 of drilling mud 110 from the mud tank 112 to an inlet of the first decanter centrifuge 124. The first decanter centrifuge 124 receives the entire flow 113 of drilling mud 110 and is operated at a relatively low RPM (as described above) so as to separate the flow 113 into a first solids underflow, or reject, portion 126 and a first fluid overflow portion 128. The first solids underflow portion 126 is primarily composed of a relatively high percentage of higher density barite particles and a relatively small percentage of lower density drill cuttings particles mixed into a slurry with a small amount of drilling fluid, whereas the first fluid overflow portion 128 is primarily made up of drilling fluid 110 with a relatively high percentage of lower density drill cuttings particles and a relatively low percentage of higher density barite particles.

Upon exiting the underflow outlet of the first decanter centrifuge 124, the first solids underflow slurry 126, which is primarily composed of recovered barite, flows to a first flow redirection apparatus 130, which is operated so as to direct the barite underflow slurry 126 to the barite mixing tank 134, as is indicated by the blackened flow branch of the first flow redirection apparatus 130 and the dashed line between the first apparatus 130 and the solids disposal tank 132. Typically, the first flow redirection apparatus 130 is a simple slide or chute that can be configured and arranged so that the first solids underflow slurry 126 is directed to the appropriate location or apparatus, such as the barite mixing tank 134 as shown in FIG. 1A, or to a solids disposal tank 132, as will be further described in conjunction with FIG. 1B below. Additionally, when the prior art system 170 is configured for barite recovery, a flow 115 of drilling mud 110 is typically generated by a second pump 138 from the mud tank 112 to the barite mixing tank 134, where it can be mixed and blended with the barite underflow slurry 126 by an agitator 136, thereby creating a blended drilling mud/barite mixture 139 that can be pumped back to the mud tank 112. In the barite recovery configuration depicted in FIG. 1A, the second pump 138 generates the flow 115 of drilling mud 110 to a second flow redirection apparatus 135, such as a three-way valve, which is in turn operated so as to direct the flow 115 to the barite mixing tank 134, as indicated by the blackened flow branch of the second flow redirection apparatus 135. Thereafter, a flow 137 of the blended drilling mud/recovered barite mixture 139 is then generated back to the mud tank 112 by a third pump 140 so that the recovered barite can be re-used for further drilling operations.

Also as shown in FIG. 1A, when the barite recovery system 170 is configured in the barite recovery mode, the first fluid overflow portion 128 exiting the overflow outlet of the first decanter centrifuge 124 flows to a third flow redirection apparatus 142, e.g., a three-way valve or flow chute, which is operated or configured so that the first overflow portion 128 is directed to an overflow staging tank 143, as indicated by the blackened flow branch of the third flow redirection apparatus 142. A fourth pump 145 is then used to pump the first overflow portion 128 from the overflow staging tank 143 to a second decanter centrifuge 144 for further solids particle separation. The second decanter centrifuge 144 receives the first fluid overflow portion 128 and is operated at a substantially higher RPM relative to that of the first centrifuge 124 (as described above) so as to separate the first overflow portion 128 into a second solids underflow, or reject, portion 146 and second fluid overflow portion 148. The second solids underflow portion 146 exiting the second centrifuge 144 typically flows into a solids disposal tank or pit 150, and is composed primarily of lower density drill cuttings particles mixed into a slurry with some amount of drilling fluid, as well as a relatively small amount of higher density barite particles that are carried over from the first centrifuge 124. The second fluid overflow portion 148 exits the second decanter centrifuge 144 as a “clean” drilling mud 110, which generally contains only relatively small amounts of either high or low density solids particles, and is returned to the mud tank 112 for mixing and blending with the recovered barite, as shown in FIG. 1A.

In some prior art applications, the second fluid overflow portion 148, i.e., the “cleaned” drilling mud 110, is returned to the suction chamber or compartment (not shown) of the mud tank 112, along with the flow 139 of blended drilling mud/recovered barite mixture. A mud pump 116 then draws the cleaned and treated drilling mud 110 through a suction line 114 from the suction chamber and pumps the treated drilling mud 110 through a discharge line 118 to a rotary line (not shown) attached to a drill string (not shown), and back down into the wellbore (not shown).

FIGS. 1B and 1C schematically depict the drilling mud treatment system 100 of FIG. 1A wherein the barite recovery system 170 is configured to process unweighted drilling mud 110. As noted previously, an unweighted drilling mud is one wherein most if not all of the solids particles remaining in the flow 113 of drilling mud 110 treated by the system represent drill cuttings particles, because no high density barite particles have been added to, or need to be recovered from, the drilling mud 110. Turning first to FIG. 1B, the barite recovery system 170 is configured so that the first and second decanter centrifuges 124 and 144 are arranged for parallel flow. More specifically, since there is no barite being recovered by the first decanter centrifuge 124, then there is no underflow slurry 126 of recovered barite being sent to the barite mixing tank 134 for the flow 115 of drilling mud 110 to be mixed with. Accordingly, the second flow redirection apparatus 135 is operated so that the flow 115 of drilling mud 110 from the mud tank 112 that is generated by the second pump 138 is directed to the second centrifuge 144 for separation, thus bypassing the barite mixing tank 134, as is indicated by the blackened flow branch of the second flow redirection apparatus 135 and the dashed line between the second apparatus 135 and the barite mixing tank 134. Meanwhile, the flow 113 of drilling mud 110 generated by the first pump 120 is still directed to the first centrifuge 124 for separation. Typically, the two centrifuges 124, 144 are operated in substantially similar fashion, e.g., at similar RPM's, so as to separate as much of the solids particles, e.g., drill cuttings, as possible from the drilling mud 110, irrespective of particle size and/or particle specific gravity.

In most applications, the first solids underflow 126 exiting the first decanter centrifuge 124 is a slurry containing a high percentage of the solids particles that initially entered the first centrifuge 124 with the flow 113, mixed together with a small amount of drilling mud 110. The first underflow slurry 126 then flows to the first flow redirection apparatus 130, which is operated and/or configured so as to direct the first underflow slurry 126 to a solids disposal tank 132. In this way, the barite mixing tank 134 is essentially bypassed, as indicated by the blackened flow branch of the first flow redirection apparatus 130 and the dashed line between the apparatus 130 and the barite mixing tank 134. Similarly, the second solids underflow 146 exiting the second decanter centrifuge 144 is also a slurry containing a high percentage of the solids particles that initially entered the second centrifuge 144 with the flow 115, mixed together with a small amount of drilling mud 110. As previously noted with respect to FIG. 1A, the second underflow slurry 146 again flows to the solids disposal tank 150.

The first and second fluid overflow portions 128, 148 typically exit the respective first and second decanter centrifuges 124, 144 as substantially “clean” drilling mud 110, that is, the overflow portions 128 and 148 generally contain only relatively small amounts of solids particles. In the system configuration depicted in FIG. 1B, the third flow redirection apparatus 142 is operated and/or configured so that the first fluid overflow portion 128 exiting the first centrifuge 124 bypasses the overflow staging tank 143 and the second centrifuge 144, as indicated by the blackened flow branch of the apparatus 142 and the dashed line between the apparatus 142 and the overflow staging tank 143. The two fluid overflow portions 128, 148 then flow together as a substantially “clean” flow 152 of drilling mud, which is directed back to the mud tank 112 for recirculation into the drilled wellbore (not shown) by the mud pump 116, as previously described.

Since the barite mixing tank 134 is bypassed, and barite is not being recovered from the drilling mud 110 in the system configuration depicted in FIG. 1B, drilling mud 110 is not circulated from the mud tank 112 to the barite mixing tank 134. Furthermore, the agitator 136 is also not operated, since there is no recovered barite or drilling mud 110 in the barite mixing tank 134 to mix and blend, nor is the third pump 140 operated, since there is no drilling mud mixture to be pumped from the barite mixing tank 134 back to the mud tank 112.

FIG. 1C schematically illustrates the drilling mud treatment system 100 wherein the barite recovery system 170 is configured differently from that shown in FIG. 1B for treating unweighted drilling mud 110. In particular, FIG. 1C depicts the barite recovery system 170 wherein the second flow redirection apparatus 135 is again operated so as to direct the flow 115 of drilling mud 110 generated by the second pump 138 to the second decanter centrifuge 144. Additionally, the first pump 120 is shut in, and therefore is not operated to direct a flow of drilling mud 110 to the first decanter centrifuge 128, as indicated by the dashed lines between the mud tank 112 and the first pump 120 and between the pump 120 and the first centrifuge 124. Furthermore, the third flow redirection apparatus 142 is also operated so as to prevent any backflow of drilling mud 110 from entering the underflow outlet of the bypassed first centrifuge 124, as indicated by the blackened flow branches of the apparatus 142 and the dashed lines between the apparatus 142 and the overflow outlet of the second centrifuge 144.

In the operational configuration of the barite recovery system 170 shown in FIG. 1C, the second decanter centrifuge 144 receives the flow 115 of drilling mud 110 and is operated so as to separate the flow 115 into a solids underflow portion 146, which is discarded into the solids disposal tank 150, and a substantially “clean” drilling fluid overflow portion 148, which is directed back to the mud tank 112 for subsequent re-use in further drilling operations. The system configuration depicted in FIG. 1C is used when the volumetric flow requirements for the drilling mud quantities necessary to support drilling operations are substantially reduced when compared to what can be treated in the parallel system flow configuration of FIG. 1B, or when the first decanter centrifuge 124 is taken out of service for maintenance and/or repair.

As noted previously, the barite recovery system generally described above has been used in many prior art applications to separate, recover, and re-use the desirable and beneficial barite particles from spent drilling mud. However, there are significant capital and operation costs, as well as safety and environment considerations, associated with the fabrication, assembly, and operation of such a prior art barite recovery system. For example, a dedicated barite recovery tank is typically required for temporarily storing the recovered barite, which includes a mud agitator for mixing and blending the recovered barite with drilling mud. Furthermore, additional mud circulation pumps are required so as to pump a substantially continuous supply of drilling mud to the barite recovery tank for mixing with the recovered barite, as well as to pump the recovered barite/drilling mud mixture back to the active mud tank. This requires that additional quantities of drilling mud be purchased and kept on hand to support the mud circulation and mixing/blending activities. Additionally, a significant amount of additional piping is required so as to make up the appropriate interconnections between the extra pieces of equipment (tanks, pumps, etc.), all of which can take up a substantial footprint in areas where plot space often comes at a premium. Moreover, operating the additional tankage, pumping, and plumbing equipment can lead to drilling mud spillage, which brings with it the environmental issues associated with any related cleanup activities, including the disposal of the additional volumes of drilling mud that are required to support the overall barite recovery operation.

The present disclosure is directed to barite recovery systems and methods of operating the same that may be used to mitigate, or possibly even eliminate, at least some of the problems associated with the prior art systems described above.

SUMMARY OF THE DISCLOSURE

The following presents a simplified summary of the present disclosure in order to provide a basic understanding of some aspects disclosed herein. This summary is not an exhaustive overview of the disclosure, nor is it intended to identify key or critical elements of the subject matter disclosed here. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later.

Generally, the subject matter disclosed herein is directed to various new and unique systems, apparatuses, and methods that may be used for treating drilling fluid so as to recover beneficial solids particles, such as barite and the like, from the drilling fluid. In one illustrative embodiment, a method for treating drilling mud is disclosed that includes, among other things, directing a first flow portion of a flow of drilling mud to a decanter centrifuge, directing a second flow portion of the flow of drilling mud to a solids particle recovery hopper, and separating an underflow from the first flow portion with the decanter centrifuge, wherein the underflow includes first solids particles having a first density. The disclosed method further includes directing the underflow to the solids particle recovery hopper, mixing the underflow with the second flow portion in the solids particle recovery hopper, and directing a flow of the mixed underflow and second flow portion from the solids particle recovery hopper to an active mud tank.

In an additional exemplary embodiment of the present disclosure, a method for treating drilling mud includes generating a flow of weighted drilling mud from an active mud tank to a first flow redirection apparatus and operating the first flow redirection apparatus to direct a first flow portion of the flow of weighted drilling mud to a first decanter centrifuge and to direct a second flow portion of the flow of weighted drilling mud to a barite recovery hopper. Additionally, the first decanter centrifuge is operated to generate a first underflow and a first overflow from the first flow portion of the flow of the weighted drilling mud, wherein the first underflow comprises barite particles and the first overflow comprises drill cuttings particles. The illustrative method further includes, among other things, directing the first underflow from the first decanter centrifuge to the barite recovery hopper, mixing the first underflow with the second flow portion of the flow of weighted drilling mud in the barite recovery hopper, and directing a flow of the mixed first underflow and second flow portion from the barite recovery hopper to the active mud tank.

In yet another illustrative embodiment, a method for treating drilling mud with a drilling mud treatment system that includes an active mud tank, at least one decanter centrifuge, and a barite recovery hopper is disclosed, wherein the method includes closing a hopper bypass gate of the barite recovery hopper to substantially prevent flow through a bottom bypass opening of the barite recovery hopper, and, with the hopper bypass gate closed to substantially prevent flow through the bottom bypass opening, treating weighted drilling mud with the drilling mud treatment system. In the disclosed exemplary embodiment, treating the weighted drilling mud includes, among other things, directing a first flow portion of a flow of the weighted drilling mud from the active mud tank to a first decanter centrifuge, directing a second flow portion of the flow of weighted drilling mud to the barite recovery hopper, and generating a first underflow from the first flow portion with the first decanter centrifuge, the first underflow including barite particles. Additionally, treating the weighted drilling mud further includes directing the first underflow to the barite recovery hopper, mixing the first underflow with the second flow portion in the barite recovery hopper, and directing a flow of the mixed first underflow and second flow portion from the barite recovery hopper to the active mud tank. The disclosed method of treating drilling mud with the drilling mud treatment system also includes opening the hopper bypass gate to allow flow through the bottom bypass opening, and, with the hopper bypass gate opened to allow flow through the bottom bypass opening, treating unweighted drilling mud with the drilling mud treatment system, wherein treating the unweighted drilling mud includes directing a flow of the unweighted drilling mud from the active mud tank to the first decanter centrifuge, and generating a second underflow from the flow of unweighted drilling mud with the first decanter centrifuge. Furthermore, the second underflow is directed to the barite recovery hopper, wherein the second underflow flows out of the barite recovery hopper through the bottom bypass opening and into a first solids disposal structure, a second overflow is generated from the flow of unweighted drilling mud with the first decanter centrifuge, and the second overflow is directed to the active mud tank.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which:

FIGS. 1A-1C are schematic flow diagrams depicting various operational configurations of an illustrative prior art barite recovery system;

FIGS. 2A-2D are schematic flow diagrams depicting illustrative embodiments of a barite recovery system in accordance with the present disclosure; and

FIGS. 3A and 3B are schematic illustrations of one exemplary embodiment of a barite recovery hopper that may be used in conjunction with various illustrative embodiments of the barite recovery systems depicted in FIGS. 2A-2D.

While the subject matter disclosed herein is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

DETAILED DESCRIPTION

Various illustrative embodiments of the present subject matter are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

The present subject matter will now be described with reference to the attached figures. Various systems, structures and devices are schematically depicted in the drawings for purposes of explanation only and so as to not obscure the present disclosure with details that are well known to those skilled in the art. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the present disclosure. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional manner that directly and unequivocally provides the special definition for the term or phrase.

As used in this description and in the appended claims, the terms “substantial” or “substantially” are intended to conform to the ordinary dictionary definition of that term, meaning “largely but not wholly that which is specified.” As such, no geometrical or mathematical precision is intended by the use of terms such as “substantially flat,” “substantially perpendicular,” “substantially parallel,” “substantially circular,” “substantially elliptical,” “substantially rectangular,” “substantially square,” “substantially aligned,” and/or “substantially flush,” and the like. Instead, the terms “substantial” or “substantially” are used in the sense that the described or claimed component or surface configuration, position, or orientation is intended to be manufactured, positioned, or oriented in such a configuration as a target. For example, the terms “substantial” or “substantially” should be interpreted to include components and surfaces that are manufactured, positioned, or oriented as close as is reasonably and customarily practicable within normally accepted tolerances for components of the type that are described and/or claimed. Furthermore, the use of phrases such as “substantially conform” or “substantially conforms” when describing the configuration or shape of a particular component or surface, such as by stating that “the configuration of the component substantially conforms to the configuration of a rectangular prism,” should be interpreted in similar fashion.

Furthermore, it should be understood that, unless otherwise specifically indicated, any relative positional or directional terms that may be used in the descriptions set forth below—such as “upper,” “lower,” “above,” “below,” “over,” “under,” “top,” “bottom,” “vertical,” “horizontal,” “lateral,” “toward,” “away,” “through,” and the like—have been included so as to provide additional clarity to the description, and should be construed in light of that term's normal and everyday meaning relative to the depiction of the components or elements in the referenced figures. For example, referring to the cross-sectional view of the in-process device depicted in FIG. 1, it should be understood that the active semiconductor layer 3 is depicted as being positioned “above” the base substrate material 1, and the buried insulating material layer 2 is depicted as being positioned “below” the active semiconductor layer 3 and “above” the base substrate material 1. Additionally, the “top” or “upper” surface of the active semiconductor layer 3 as shown in FIG. 1 is depicted as being substantially “horizontally” oriented, and in the cross-sectional view of FIG. 2, the device isolation trenches 4 are shown as extending “below” the “bottom” or “lower” surface of the buried insulating material layer 2. However, it should be understood that such descriptions are for reference only based on how the various elements are arranged relative to one another in the figures, and therefore should not be construed as limiting in any way on how the depicted structures or components might actually be oriented during manufacture, assembly, and/or use.

Generally, the subject matter disclosed herein provides various embodiments of systems, components, and methods that may be used to treat drilling fluid (i.e., drilling mud) to recover high specific gravity solids particles, such as barite and the like, from the spent drilling mud.

FIGS. 2A-2D are schematic flow diagrams that illustrate a drilling mud treatment system 200 in accordance with the present that includes a solids removal and recovery system 270 that can be configured to treat both weighted and unweighted drilling fluids. In the exemplary embodiment of the solids removal and recovery system 270 depicted in FIG. 2A, the system 270 is in an operational configuration that allows desirable high specific gravity particles, such as barite and the like, to be recovered from a drilling mud 210 and circulated back to the active mud system for re-use in further drilling operations. For simplicity of description, the solids removal and recovery system 270 may sometimes be referred to hereinafter as a barite recovery system 270.

As shown in FIG. 2A, drilling mud 210 that is returned from a drilled wellbore (not shown), sometimes referred to herein as “spent drilling mud,” may flow through a spent mud flow line 202 to a primary solids separation apparatus 204, e.g., a shale shaker or other vibratory separator, where an initial separation step may be performed so as to remove large drill cuttings particles 207 from the mud 210. The separated drilling cuttings 207 may then be directed to a drilling cuttings tank or pit 208, and the portions of the drilling mud 210 passing through the various screening decks of the shale shaker 204 may flow down to a sump 206, after which is it directed to the active mud system tank 212 for further processing.

In certain illustrative embodiments of the drilling mud treatment system 200, a flow of the drilling mud 210 may be directed through one or more intermediate mud treatment and/or solids separation apparatuses, which are collectively depicted schematically in FIG. 2A as system 260. In some embodiments, the system 260 may include, for example, an apparatus for removing entrained gases from the drilling mud 210 (e.g., vacuum or atmospheric degasser), one or more apparatus(es) for removing sand and/or silt from the mud 210 (e.g., desander and/or desilter hydrocyclones), the design and operation of which are well known in the art, and as such will not be further described herein.

As noted above, the system 270 of FIG. 2A is depicted in a configuration that is adapted for recovering desirable and beneficial high density solids particles, e.g., barite, from the drilling mud 210 for re-use in further drilling operations. In some exemplary embodiments, the barite recovery system 270 may include a first pump 220 that is adapted to circulate spent drilling mud 210 through a first decanter centrifuge 224 and a second pump 243 that is adapted to circulate spent drilling mud 210 through a second decanter centrifuge 244, each of which may be operated as required to remove different density solids particles from the mud 210, as will be further described below. Additionally, the barite recovery system 270 may also include a barite recovery hopper 280 that, in at least some configurations, may be adapted to mix recovered barite with a flow of drilling mud during the barite recovery process, and direct the recovered barite/drilling mud mixture 229 back to the active rig mud tank 212, as will also be described in further detail below. Also as shown in FIG. 2A, various illustrative embodiments of the barite recovery system 270 disclosed herein may include solids disposal pits or tanks 234 and 250, which, depending on the specific operational configuration of the system 270, may be used for temporary storage of the solids that are removed from the mud 210 using the respective first and second centrifuges 224 and 244 prior to eventual disposal. It should be understood that, depending on the specific arrangement of the first and second centrifuges, the solids disposal tanks 234 and 250 may be combined as a single solids disposal tank, however for simplicity, use and operation of each of the tanks 234 and 250 will be described separately below. Additionally, the barite recovery system may also include a plurality of flow redirection apparatuses 223, 242, and 243, which may be operated and/or configured as desired so as to direct various flows of drilling mud and/or decanter centrifuge overflows to appropriate locations or other apparatuses within the system 270, as will be further described below.

In some illustrative embodiments, the pump 220 may be operated to generate a flow 213 of drilling mud 210 from the mud tank 212 to a first flow redirection apparatus 223, such as a three-way valve and the like. As shown in FIG. 2A, the first flow redirection apparatus 223 may be operated so that a first flow portion 213 a of the flow 213 of drilling mud 210 being pumped from the mud tank 212 by the pump 220 may be directed to the first decanter centrifuge 224, whereas a second flow portion 213 b of the flow 213 may be directed to bypass the first centrifuge 224. Additionally, in certain aspects, the second flow portion 213 b that bypasses the first centrifuge 224 may be circulated through the barite recovery hopper 280 (see, FIGS. 3A and 3B for additional details), where it may mix with and flush any barite that is recovered by the first centrifuge 224 back to the active mud tank 212, as will be further described below.

Returning now to the barite recovery system 270 shown in FIG. 2A, the first decanter centrifuge 224 may be adapted to receive the first flow portion 213 a of drilling mud 210 directed thereto by the second flow redirection apparatus 223. In certain embodiments, the first centrifuge may be operated at a relatively low RPM (as previously described) so as to thereby separate the first flow portion 213 a into a first solids underflow, or reject, portion 226 and a first fluid overflow portion 228. Depending on the operational parameters of the first decanter centrifuge, the first solids underflow portion 226 may primarily be composed of a relatively high percentage of barite, i.e., higher density solids particles, that may be mixed together with a small amount of drilling fluid so as to form a first solids underflow slurry 226. In some aspects, the first solids underflow slurry portion 226 may also include a relatively low percentage of drill cuttings, i.e., lower density solids particles. In certain other embodiments, the first fluid overflow portion 228 may primarily be made up of the base fluid of the drilling mud 210 as well as an amount of unseparated overflow solids. Depending on the specific operational parameters of the first decanter centrifuge 224, the unseparated overflow solids carried over with the first fluid overflow portion 228 may contain, for example, a relatively high percentage of drill cuttings, i.e., lower specific gravity solids particles, as well as, in some cases, a relatively low percentage of barite, i.e., higher specific gravity solids particles.

Upon exiting the underflow outlet of the first decanter centrifuge 224, the first solids underflow slurry portion 226, which, as noted above, may be primarily composed of recovered barite, may then flow into the barite recovery hopper 280. As depicted in FIG. 2A, the barite recovery hopper 280 is in a closed barite recovery configuration, thus allowing the recovered barite to be accumulated and subsequently re-used for further drilling operations. In at least some embodiments, the first solids underflow slurry portion 226 flowing from the first centrifuge 224 may then be mixed together in the barite recovery hopper 280 with the second flow portion 213 b of drilling mud 210 so as to create a mixture 229 of recovered barite and drilling mud. A flow 227 of the recovered barite/mud mixture 229 from the barite recovery hopper 280 may then be directed back to the active mud tank 212, as shown in FIG. 2A. FIGS. 3A and 3B, which schematically illustrate some detailed aspects of one exemplary embodiment of a barite recovery hopper 280 in accordance with the present disclosure, are described below.

FIG. 3A schematically depicts the exemplary barite recovery hopper 280 in the barite recovery configuration of FIG. 2A. As shown in FIG. 3A, the barite recovery hopper 280 may include a body or shell 281 having a substantially open top 288 that is adapted to receive the first solids underflow portion 226 flowing from the first decanter centrifuge 224. In certain embodiments, the open top 288 of the barite recovery hopper 280 may be attached and sealed to a solids discharge chute 224 c (schematically depicted by dashed lines in FIG. 3A) of the first centrifuge 224 so as to substantially prevent leakage while the barite recovery system 270 is being operated in the barite recovery mode. Additionally, the shell 281 may have a mud circulation inlet 282 that is adapted to receive the second flow portion 213 b of drilling mud 210 bypassing the first decanter centrifuge 224 (see, FIG. 2A), and a mud circulation outlet 283 that is adapted to direct a flow 227 of the recovered barite/mud mixture 229 back to the mud tank 212. In certain embodiments, the mud circulation inlet 282 may include an internal projection portion 282 p that may act as a jet or gun nozzle so as to facilitate a more thorough and complete mixing of the redirected bypass flow 213 b entering the nozzle 282 from the first flow redirection apparatus 223 with the recovered barite exiting the first decanter centrifuge 224. See, FIG. 2A. Furthermore, in at least some embodiments of the barite recovery mode, an amount of the recovered barite/mud mixture 229 may sometimes accumulate inside of the barite recovery hopper 280, as shown in FIG. 3A.

In some illustrative configurations, the barite recovery hopper 280 may have a hopper bypass gate 284 that is adapted to be in a closed position so as to seal a bottom opening 289 (see, FIG. 3B) of the shell 281 while the hopper 280 is configured for operation in a barite recovery mode. In some embodiments, the shell 281 may include at least one seal plate 286 that substantially surrounds the bottom opening 289, and a sealing element or gasket 287 may be positioned between the seal plate 286 and the hopper bypass gate 284 so as to substantially seal the bottom opening 289 when the gate 284 is in a closed barite recovery mode, thereby reducing the likelihood of drilling mud leakage or bypass. During the barite recovery operation, the closed and sealed hopper bypass gate 284 generally acts to facilitate collection of the recovered barite in the hopper 280 so that it can mix and blend with the second flow portion 213 b of the drilling mud 210 being circulated by the pump 220. Furthermore, the second flow portion 213 b entering the barite recovery hopper 280 through the mud inlet 282 may also act to substantially continuously flush a flow 227 of the recovered barite/mud mixture 229 out of the hopper 280 and back to the mud tank 212 during barite recovery operations.

In certain embodiments, the hopper bypass gate 284 may be opened when the barite recovery system 270 is configured in a hopper bypass mode for treating unweighted drilling mud, thereby allowing the separated first underflow solids portion 226 to pass completely through, i.e. bypass, the barite recovery hopper, as will be further described in conjunction with FIGS. 2B-2D below. For example, the hopper bypass gate 284 may be pivotably attached to the shell 281, such as by one or more pinned or hinged connections 284 h, which may thereby allow the hopper bypass gate 284 to be swung open to a hopper bypass position, as shown FIG. 3B. Additionally, the barite recovery hopper 280 may include one or more gate latches 285 (schematically depicted in FIGS. 3A and 3B) that are adapted to maintain the hopper bypass gate 284 in a closed position during barite recovery operations. In some embodiments, the latch(es) 285 may be also be pivotably attached to the shell 281, such as by one or more pinned or hinged connections 285 h, so that the latch(es) 285 may be pivoted rotated away from a latching position against the hopper bypass gate 284, thereby allowing the gate 284 to be opened for hopper bypass operations.

Returning now to FIG. 2A, when the barite recovery system 270 is configured in the barite recovery mode, the first fluid overflow portion 228 exiting the overflow outlet of the first decanter centrifuge 224 may then flow to a second flow redirection apparatus 242, such as a three-way valve, a re-configurable flow chute or flexible flowline hose, and the like. As shown in FIG. 2a , the second flow redirection apparatus 242 may be operated so that substantially the entirety of the first fluid overflow portion 228 is directed to the suction side of a second pump 245 that is adapted to feed the first fluid overflow portion 228 to the inlet of the second decanter centrifuge 244, as indicated by the blackened flow branch of the apparatus 242. For example, in at least some embodiments, the second flow redirection apparatus 242 may be operated and/or configured so as to direct the first fluid overflow portion 228 to a third flow redirection apparatus 243, such as a three-way valve, that is positioned on the suction side of the second pump 245, and which may be operated so as to direct substantially the entirety of the fluid overflow 228 exiting the second decanter centrifuge 224 to the suction side of the pump 245, as indicated by the blackened flow branch of the third apparatus 243. Furthermore, in certain embodiments, the second decanter centrifuge 244 may receive the first fluid overflow portion 228 from the second pump 245 and be operated at a substantially higher RPM relative to that of the first centrifuge 224 (as described above) so as to thereby separate the first overflow portion 228 into a second solids underflow, or reject, portion 246 and second fluid overflow portion 248.

During some operations of the barite recovery system 270, the second solids underflow portion 246 exiting the second centrifuge 244 is directed to flow into a solids disposal tank or pit 250. Depending on the specific operating parameters of the second decanter centrifuge 244, the second solids underflow portion 246 may be composed primarily of lower density solids particles, e.g., drill cuttings and the like, mixed into a slurry with a small amount of drilling fluid. In certain aspects, the second solids underflow portion 246 may also include a relatively small amount of higher density solids particles, e.g., barite, that may have been carried over from the first centrifuge 224. Furthermore, the second fluid overflow portion 248 may exit the second decanter centrifuge 244 as a substantially “clean” drilling mud 210, that is, one which generally contains only relatively small amounts of either high or low density solids particles. As shown in FIG. 2A, the second fluid overflow portion 248 exiting the second centrifuge 244 may then be returned directly to the mud tank 212 for mixing and blending with the recovered barite prior to being re-used for subsequent drilling operations.

In some embodiments, the second fluid overflow portion 248, i.e., the “cleaned” drilling mud 210, is returned to the suction chamber or compartment (not shown) of the mud tank 212, along with the flow 227 of recovered barite/mud mixture 229. Thereafter, a mud pump 216 may be operated to draw the cleaned and treated drilling mud 210 through a suction line 214 from the suction chamber of the mud tank 212 and to pump the drilling mud 210 through a discharge line 218 and back down into the drilled wellbore (not shown).

FIGS. 2B-2D schematically depict various illustrative configurations of the barite recovery system 270 shown in FIG. 2A that may be used to process unweighted drilling mud 210. In such embodiments, since no high density barite particles have been intentionally added to the drilling mud 210, substantially most of the solids particles present in the flow of drilling mud 210 to the system 270 represent drill cuttings, e.g., low density solids particles.

In some illustrative embodiments, the barite recovery system 270 may be configured with the first and second decanter centrifuges 224 and 244 arranged for parallel flow, that is, so that both decanter centrifuges 224, 244 receive and treat a flow of drilling mud that has a substantially similar composition. For example, as shown in FIG. 2B, the first flow redirection apparatus may be operated so as to direct substantially the entirety of the flow 213 of drilling mud 210 pumped from the mud tank 212 by the first pump 220 to the first decanter centrifuge 224, thus bypassing the barite recovery hopper 280. For reference, this barite recovery hopper bypass mode is indicated in FIG. 2B by the blackened flow branch of the first flow redirection apparatus 223 and the dashed line between the apparatus 223 and the mud circulation inlet 282 (see, FIG. 3A) of the barite recovery hopper 280. Additionally, the second and third flow redirection apparatuses 242, 243 may also be operated and/or configured so that the suction side of second pump 245 is in fluid communication with the active mud tank 212, as indicated by the blackened flow branches of the second and third flow redirection apparatuses 242, 243 and the dashed line between the two apparatuses 242, 243. In this way, the second pump 245 may generate a second flow 215 of drilling mud 210 from the mud tank 212 to the second decanter centrifuge 244, as shown in FIG. 2B.

For example, in one illustrative embodiment, flow between the second and third flow redirection apparatuses 242, 243 may be accomplished in the barite recovery mode of FIG. 2A by way of a flexible flowline hose and the like. In such embodiments, when flow to the suction side of the second pump 245 is reconfigured so as to draw a flow 215 of drilling mud 210 directly from the tank 212, the flexible flowline hose between the two flow redirection apparatuses 242, 243 may be disconnected from the second flow redirection apparatus 242 and connected directly to a suction nozzle (not shown) on the mud tank 212. However, it should be appreciated by those of ordinary skill after a complete reading of the present disclosure that other valving and/or plumbing configurations may also be utilized.

In the exemplary embodiment schematically depicted in FIG. 2B, the first and second centrifuges 224 and 244 may therefore be arranged in parallel, such that the composition of the drilling mud 210 received by each via the respective flows 213 and 215 may be substantially the same. Furthermore, in some embodiments, the first and second centrifuges 224, 244 may be operated based upon substantially similar operational parameters, such as mud feed rate, rotational speed (RPM's), and the like, so that as much of the solids particles, e.g., drill cuttings, as possible may be removed from the drilling mud 210, irrespective of particle size and/or particle specific gravity. However, it should be understood that each centrifuge 224, 244 may be operated using substantially different operational parameters, depending on the overall solids particle separation requirements established for the particular application.

For example, in certain embodiments of the configuration illustrated in FIG. 2B the first decanter centrifuge 224 may be operated so as to separate the flow 213 into a first solids underflow portion 226 and a first fluid overflow portion 228. Depending on the operational parameters of the first centrifuge 224, the first solids underflow portion 226 may be, for example, a slurry containing a very high percentage of the solids particles that initially entered the first centrifuge 224 mixed together with a small amount of drilling fluid, whereas the first fluid overflow portion 228 may be a substantially “clean” drilling mud 210 that generally contains only relatively small amounts solids particles, and may therefore be in condition for re-use in further drilling operations. Furthermore, since there is no barite to recover from the drilling mud 210, the barite recovery hopper 280 may be configured in the hopper bypass mode, that is, wherein the hopper bypass gate 284 has been opened, as shown in FIG. 2B. See also, FIG. 3B. In the hopper bypass configuration, the first solids underflow portion 226 exiting the first decanter centrifuge 224 may thus be allowed to flow through the barite recovery hopper 280 to a solids disposal tank or pit 234, thereby bypassing the barite recovery hopper 280 substantially without being held up. Also, and as previously noted, the second flow redirection apparatus 242 may be operated and/or configured so that the first fluid overflow portion 228 exiting the first centrifuge 224 bypasses the second centrifuge 244, as indicated in FIG. 2B by the blackened flow branch of the apparatus 242 and the dashed line between the second flow redirection apparatus 242 and the third flow redirection apparatus 243.

Similarly, the second decanter centrifuge 244 may be operated so as to separate the flow 215 into a second solids underflow portion 246 and a second fluid overflow portion 248, each of which may have substantially similar characteristics and compositions to the respective first solids underflow portion 226 and first fluid overflow portion 228. As shown in FIG. 2B, the second solids underflow portion 246 may then flow into the solids disposal tank 250. Furthermore, the second fluid overflow portion 248 exiting the second centrifuge 244 and the first fluid overflow portion 228 bypassing the second centrifuge 244 may then flow together so as to form a substantially “clean” flow 252 of drilling mud, which may in turn be directed back to the drilling rig's active mud tank 212 for recirculation into the drilled wellbore (not shown) by the mud pump 216, as previously described.

FIG. 2C schematically illustrates the barite recovery system 270 in a further exemplary configuration for treating unweighted drilling mud 210 that is different from that shown in FIG. 2B. In particular, FIG. 2C depicts the barite recovery system 270 wherein the third flow redirection apparatus 243 is again operated and/or configured so as to direct the flow 215 of drilling mud 210 to the second pump 243 and from there to the second decanter centrifuge 244. On the other hand, the first pump 220 may be shut in, that is, not operated to direct a flow of drilling mud 210 to the first flow redirection apparatus 223 and the first decanter centrifuge 228, as indicated by the dashed lines between the mud tank 212 and the first pump 220 and between the first pump 220 and the first apparatus 223. Additionally, since both the first decanter centrifuge 224 and the barite recovery hopper 280 are bypassed in the depicted system configuration, the position of the hopper bypass gate 284 (closed or open) does not affect the treatment of the flow 215 of drilling mud 210. Accordingly, the hopper bypass gate may be in either a closed position or an open position, (open position is indicated by a dashed line in FIG. 2C). Furthermore, in some embodiments, the second and third flow redirection apparatuses 242, 243 may be operated and/or configured so as to prevent any backflow of drilling mud 210 or overflow 248 exiting the second decanter centrifuge 244 from entering the underflow outlet of the first decanter centrifuge 224. For reference, this backflow prevention configuration is indicated by the blackened flow branches of the apparatuses 242, 243, the dashed line between the two flow redirection apparatuses 242, 243, and the dashed lines between the apparatus 242 and the inlet and fluid overflow outlet of the second decanter centrifuge 244.

In the operational configuration of the barite recovery system 270 shown in FIG. 2C, the second decanter centrifuge 244 may be adapted to receive substantially the entire flow 213 of drilling mud 210 generated by the pump 220. In some embodiments, the second decanter centrifuge 244 may be operated so as to separate the flow 213 into a solids underflow portion 246, which may be discarded into the solids disposal tank 250 as previously noted, and a substantially “clean” drilling fluid overflow portion 248, which may be directed back to the mud tank 212 for subsequent re-use in further drilling operations. The configuration of the barite recovery system 270 depicted in FIG. 2C may sometimes be used when the volumetric flow requirements for the drilling mud quantities necessary to support drilling operations are substantially reduced, as compared to what can be readily treated in the parallel flow system configuration of FIG. 2B, or when the first decanter centrifuge 224 is taken out of service for maintenance and/or repair.

FIG. 2D schematically illustrates the barite recovery system 270 in yet a further exemplary configuration that may be used treating unweighted drilling mud 210 that is different from the configurations depicted in FIGS. 2B and 2C. For example, as shown in FIG. 2D, the barite recovery system 270 may be configured so that the first pump 220 is operated to generate a flow 213 of drilling mud 210 to the first flow redirection apparatus 223. Furthermore, the first flow redirection apparatus may be operated and/or configured so as to direct substantially the entirety of the flow 213 to the first decanter centrifuge 224, in similar fashion to that shown in FIG. 2B and described above. Additionally, the second pump 245 may be shut in and the second and third flow redirection apparatuses 242 and 243 may both be operated and/or configured so that the second decanter centrifuge 248 is bypassed, i.e., not in operation. For reference, this second decanter centrifuge bypass mode is indicated in FIG. 2D by the blackened flow branches of the second and third flow redirection apparatuses 242, 243 and the dashed lines between the mud tank 212 and the third flow redirection apparatus 243, between the respective apparatuses 242, 243, and between the second apparatus 243, the second pump 245, and the second centrifuge 244. Moreover, in at least some embodiments, an additional flow apparatus 249 may positioned downstream of the overflow outlet of the second centrifuge 244, and may also be operated so as to prevent any backflow of drilling mud 210 exiting the overflow outlet of the first centrifuge 224 from entering the over outlet of the second decanter centrifuge 244, as is indicated by the blackened flow branches of the flow control apparatus 249.

In the operational configuration of the barite recovery system 270 shown in FIG. 2D, the first decanter centrifuge 224 may be adapted to receive substantially the entire flow 213 of drilling mud 210 generated by the pump 220, as noted above. Furthermore, the first decanter centrifuge 224 may be operated so as to separate the flow 213 into a solids underflow portion 226, which may be discarded into the solids disposal tank 234 while hopper bypass gate 284 of the barite recovery hopper 280 is opened to a hopper bypass position as previously described, and a substantially “clean” drilling fluid overflow portion 228, which may be directed to the third flow redirection apparatus 242, which is operated so as to send the “clean” drilling fluid overflow portion 228 back to the mud tank 212 for subsequent re-use in further drilling operations. As with the system configuration depicted in FIG. 2C above, the system configuration of FIG. 2D may also be used for those applications wherein the volumetric flow requirements for the drilling mud quantities are substantially reduced as compared to what can be treated in the parallel flow system configuration of FIG. 2B, or when the second decanter centrifuge 244 is shut down for maintenance and/or repair.

As may be appreciated by those of ordinary skill after a complete reading of the present disclosure, the barite recovery system 270 and barite recovery hopper 280 disclosed herein address several of the various shortcomings associated with the prior art barite recovery systems. For example, the exemplary barite recovery systems 270 described above eliminates at least two of the mud circulation pumps that are used in the prior art barite recovery system 170, including the pump 140 that is used to pump the flow 137 of blended drilling mud/recovered barite mixture 139 from the barite mixing tank 134 to the mud tank 112, and the pump 145 that is used to pump the first fluid underflow portion 128 from the underflow staging tank 143 to the second centrifuge 144. Furthermore, the additional piping that is necessary to interconnect the mud circulation pumps 140 and 145 to the other equipment of the prior art system 170 may also eliminated. Additionally, the barite mixing tank 134 and the overflow staging tank 143 of the prior art barite recovery system 170 are both eliminated, as is the mud agitator 136 that is used to mix and blend recovered barite with drilling mud in the barite mixing tank 134. Instead, the presently disclosed barite recovery system 270 is adapted to utilize only a single pump 220 to feed drilling mud 210 to the first decanter centrifuge 224, as well as to circulate the drilling mud 210 through the barite recovery hopper 280 and blend the drilling mud 210 with recovered barite in the hopper 280. Moreover, only a single pump 245 is used to feed the second decanter centrifuge 244, whether during a barite recovery operation, or when treating unweighted drilling mud.

Accordingly, the first pump 220 of the barite recovery system 270 may therefore be used to perform multiple functional operations with the first decanter centrifuge 224—e.g., feeding, flushing, and blending—and the second pump 245 may be used for feeding the second decanter centrifuge 244 when treating either weighted or unweighted drilling muds, whereas multiple pumps 120, 138, 140, and 145 are required to perform the same functional operations in the prior art barite recovery system 170. Additionally, the use of the single pump 220 for the feed, flush, and blending operations associated with the barite recovery mode of operation substantially eliminates the need for additional volumes of drilling mud, as is required for operating the barite mixing tank 134 and mud circulation pumps 138, 140 of the prior art system 170. Moreover, since the barite recovery hopper 280 of the system 270 may be directly attached and sealed to the first decanter centrifuge 224, as opposed to the open-topped barite mixing tank 134 of the prior art system 170, the likelihood for drilling mud spillage occurring with the system 270 during barite recovery operations may be substantially reduced, together with the costs associated with any resulting cleanup requirements and drilling mud replacement.

As a result, the subject matter disclosed herein provides detailed aspects of various systems, apparatuses, and methods that may be used for recovering beneficial solids particles, such as barite and the like, from spent drilling mud for re-use in wellbore drilling operations.

The particular embodiments disclosed above are illustrative only, as the subject matter defined by the appended claims may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. For example, some or all of the process steps set forth above may be performed in a different order. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the claimed subject matter. Note that the use of terms, such as “first,” “second,” “third” or “fourth” to describe various processes or structures in this specification and in the attached claims is only used as a shorthand reference to such steps/structures and does not necessarily imply that such steps/structures are performed/formed in that ordered sequence. Of course, depending upon the exact claim language, an ordered sequence of such processes may or may not be required. Accordingly, the protection sought herein is as set forth in the claims below. 

What is claimed:
 1. A method for treating drilling mud, the method comprising: directing a first flow portion of a flow of drilling mud to a decanter centrifuge; directing a second flow portion of said flow of drilling mud to a solids particle recovery hopper; separating an underflow from said first flow portion with said decanter centrifuge, said underflow comprising first solids particles having a first density; directing said underflow to said solids particle recovery hopper; mixing said underflow with said second flow portion in said solids particle recovery hopper; and directing a flow of said mixed underflow and second flow portion from said solids particle recovery hopper to an active mud tank.
 2. The method of claim 1, further comprising separating an overflow from said first flow portion with said decanter centrifuge, said overflow comprising second solids particles having a second density that is less than said first density.
 3. The method of claim 2, wherein said first drilling mud is a weighted drilling mud, wherein said first solids particles having said first density are barite particles, wherein said second solids particles having said second density are drill cuttings particles, and wherein said solids particle recovery hopper is a barite recovery hopper.
 4. The method of claim 2, wherein said overflow is a first overflow, the method further comprising: directing said first overflow to a second decanter centrifuge; separating a second underflow from said first overflow with said second decanter centrifuge, said second underflow comprising at least a portion of said second solids particles; separating a second overflow from said first overflow with said second decanter centrifuge, said second overflow comprising at least a base drilling fluid; and directing a flow of said second overflow to said active mud tank.
 5. A method for treating drilling mud, the method comprising: generating a flow of weighted drilling mud from an active mud tank to a first flow redirection apparatus; operating said first flow redirection apparatus to direct a first flow portion of said flow of weighted drilling mud to a first decanter centrifuge and to direct a second flow portion of said flow of weighted drilling mud to a barite recovery hopper; operating said first decanter centrifuge to generate a first underflow and a first overflow from said first flow portion of said flow of weighted drilling mud, wherein said first underflow comprises barite particles and said first overflow comprises first drill cuttings particles; directing said first underflow from said first decanter centrifuge to said barite recovery hopper; mixing said first underflow with said second flow portion of said flow of weighted drilling mud in said barite recovery hopper; and directing a flow of said mixed first underflow and second flow portion from said barite recovery hopper to said active mud tank.
 6. The method of claim 5, further comprising: directing said first overflow to a second decanter centrifuge; operating said second decanter centrifuge to generate a second underflow comprising at least a portion of said first drill cuttings particles and to generate a second overflow comprising at least a base drilling fluid; and directing said second overflow to said active mud tank.
 7. The method of claim 6, further comprising directing said second underflow to a solids disposal structure.
 8. The method of claim 5, wherein mixing said first underflow with said second flow portion of said first flow of weighted drilling mud in said barite recovery hopper comprises closing a hopper bypass gate of said barite recovery hopper to seal a bottom bypass opening of said barite recovery hopper and to prevent drilling mud materials from flowing out of said barite recovery hopper through said bottom bypass opening.
 9. The method of claim 8, further comprising opening said hopper bypass gate to allow drilling mud materials to flow out of said barite recovery hopper through said bottom bypass opening.
 10. The method of claim 9, further comprising: generating a first flow of unweighted drilling mud to said first decanter centrifuge, said first flow of unweighted drilling mud comprising second drill cuttings particles and a first base drilling fluid; operating said first decanter centrifuge to generate a first second underflow comprising at least a portion of said second drill cuttings particles and to generate a second overflow comprising at least a portion of said first base drilling fluid; and directing said second underflow to a first solids disposal structure and directing said second overflow to said active mud tank.
 11. The method of claim 10, wherein generating said first flow of unweighted drilling mud to said first decanter centrifuge comprises pumping said first flow of unweighted drilling mud from said active mud tank to said first flow redirection apparatus and operating said first flow redirection apparatus to bypass said barite recovery hopper and to direct substantially an entirety of said first flow of unweighted drilling mud to said first decanter centrifuge.
 12. The method of claim 10, further comprising: directing a second flow of unweighted drilling mud to a second decanter centrifuge, said second flow of unweighted drilling mud comprising third drill cuttings particles and a second base drilling fluid; operating said second decanter centrifuge to generate a third underflow comprising at least a portion of said third drill cuttings particles and to generate a third overflow comprising at least a portion of said second base drilling fluid; and directing said third underflow to a second solids disposal structure and directing said third overflow to said active mud tank.
 13. The method of claim 12, wherein generating said second flow of unweighted drilling mud to said second decanter centrifuge comprises: pumping said second flow of unweighted drilling mud from said active mud tank to a second flow redirection apparatus; and operating said second flow redirection apparatus to direct substantially an entirety of said second flow of unweighted drilling mud to said second decanter centrifuge.
 14. The method of claim 12, wherein said first decanter centrifuge and said second decanter centrifuge are arranged for parallel flow of said first flow of unweighted drilling mud and said second flow of unweighted drilling mud, respectively.
 15. The method of claim 9, further comprising: directing a flow of unweighted drilling mud to a second decanter centrifuge, said flow of unweighted drilling mud comprising second drill cuttings particles and a base drilling fluid; operating said second decanter centrifuge to generate a second underflow comprising at least a portion of said second drill cuttings particles and to generate a second overflow comprising at least a portion of said base drilling fluid; and directing said second underflow to a second solids disposal structure and directing said second overflow to said active mud tank.
 16. The method of claim 15, wherein generating said flow of unweighted drilling mud to said second decanter centrifuge comprises: pumping said flow of unweighted drilling mud from said active mud tank to a second flow redirection apparatus; and operating said second flow redirection apparatus to direct substantially an entirety of said flow of unweighted drilling mud to said second decanter centrifuge.
 17. The method of claim 16, further comprising operating said first flow redirection apparatus to prevent substantially any flow of said unweighted drilling mud from said active mud tank to either said first decanter centrifuge or said barite recovery hopper.
 18. A method for treating drilling mud with a drilling mud treatment system that comprises an active mud tank, at least one decanter centrifuge, and a barite recovery, hopper, the method comprising: closing a hopper bypass gate of said barite recovery hopper to substantially prevent flow through a bottom bypass opening of said barite recovery hopper; with said hopper bypass gate closed to substantially prevent flow through said bottom bypass opening, treating weighted drilling mud with said drilling mud treatment system, wherein treating said weighted drilling mud comprises: directing a first flow portion of a flow of said weighted drilling mud from said active mud tank to a first decanter centrifuge; directing a second flow portion of said flow of weighted drilling mud to said barite recovery hopper; generating a first underflow from said first flow portion with said first decanter centrifuge, said first underflow comprising barite particles; directing said first underflow to said barite recovery hopper; mixing said first underflow with said second flow portion in said barite recovery hopper; and directing a flow of said mixed first underflow and second flow portion from said barite recovery hopper to said active mud tank; opening said hopper bypass gate to allow flow through said bottom bypass opening; and with said hopper bypass gate opened to allow flow through said bottom bypass opening, treating unweighted drilling mud with said drilling mud treatment system, wherein treating said unweighted drilling mud comprises: directing a flow of said unweighted drilling mud from said active mud tank to said first decanter centrifuge; generating a second underflow from said flow of unweighted drilling mud with said first decanter centrifuge, said second underflow comprising first drill cuttings particles; directing said second underflow to said barite recovery hopper, said second underflow flowing out of said barite recovery hopper through said bottom bypass opening and into a first solids disposal structure; generating a first overflow from said flow of unweighted drilling mud with said first decanter centrifuge, said first overflow comprising a first base drilling fluid; and directing said first overflow to said active mud tank.
 19. The method of claim 18, wherein treating said weighted drilling mud further comprises: generating a second overflow from said first flow portion of weighted drilling mud with said first decanter centrifuge, said second overflow comprising second drill cuttings particles; directing said second overflow to a second decanter centrifuge; generating a third underflow from said second overflow with said second decanter centrifuge, said third underflow comprising at least a portion of said second drill cuttings particles; directing said third underflow to a second solids disposal structure; generating a third overflow from said second overflow with said second decanter centrifuge, said third overflow comprising at least a second base drilling fluid; and directing said third overflow to said active mud tank.
 20. The method of claim 19, wherein treating said unweighted drilling mud further comprises: directing a second flow of unweighted drilling mud from said active mud tank to said second decanter centrifuge; generating a fourth underflow from said second flow of unweighted drilling mud with said second decanter centrifuge, said fourth underflow comprising third drill cuttings particles; directing said fourth underflow to said second solids disposal structure; generating a fourth overflow from said second flow of unweighted drilling mud with said second decanter centrifuge, said fourth overflow comprising a third base drilling fluid; and directing said fourth overflow to said active mud tank. 